Yellow lens???

robert · 12-13-2012, 07:44 AM

I know some of the old pentax lenses can yellow with age. I'm wondering if it is just certain types ? Which types? And is there a cure for a lens thats turned yellow with age?...Thanks Bob

stevebrot · 12-13-2012, 08:42 AM

There are many threads on this site and on the Web dealing with this issue. In short, the yellowing is most often related to radioactive rare earth elements (thorium) in some of the optical elements. With time the glass yellows. For Pentax lenses, I believe that the problem is limited to various models and focal length Super-Takumar and SMC/S-M-C Takumar. While the Takumars have the famous reputation for radioactivity and yellowing, it would be good to note that the problem is wide-spread among lenses of many brands made during the 60s and into the early 1970s. The reputed fix is extended exposure to UV light. Again, Google is your friend.

Steve

memetph · 12-16-2012, 06:22 AM

I could read reports about this problem only for the ST 1.4 50mm and the 1.8 55mm. There are films on Youtube how to solve this problem thanks to UV.
To check your lens just shoot a white sheet of paper.
I have three ST 1.8 55mm ,none of them are concerned.I have 4 other SMC which do not have this problem.
You should not worry .

Philippe

12-13-2012, 07:44 AM	#1
robert Veteran Member Join Date: Jan 2007 Location: ohio Posts: 336	Yellow lens??? I know some of the old pentax lenses can yellow with age. I'm wondering if it is just certain types ? Which types? And is there a cure for a lens thats turned yellow with age?...Thanks Bob

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12-13-2012, 08:42 AM	#2
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	There are many threads on this site and on the Web dealing with this issue. In short, the yellowing is most often related to radioactive rare earth elements (thorium) in some of the optical elements. With time the glass yellows. For Pentax lenses, I believe that the problem is limited to various models and focal length Super-Takumar and SMC/S-M-C Takumar. While the Takumars have the famous reputation for radioactivity and yellowing, it would be good to note that the problem is wide-spread among lenses of many brands made during the 60s and into the early 1970s. The reputed fix is extended exposure to UV light. Again, Google is your friend. Steve

12-16-2012, 06:22 AM	#3
memetph New Member Join Date: Dec 2012 Posts: 1	I could read reports about this problem only for the ST 1.4 50mm and the 1.8 55mm. There are films on Youtube how to solve this problem thanks to UV. To check your lens just shoot a white sheet of paper. I have three ST 1.8 55mm ,none of them are concerned.I have 4 other SMC which do not have this problem. You should not worry . Philippe